Radar receiver sensitivity control system



Nov. 6, 1951 A. FREE ETAL 2,573,762

RADAR RECEIVER SENSITIVITY coNTRoL SYSTEM Filed March 27, 1946 3Sheets-Sheet l N0V- 6, 1951 A. L. FREE HAL RADAR RECEIVER SENSITIVITYCONTROL SYSTEM 5 Sheets-Sheet Filed March 27, 194e g D XSQK un nu N Nov.6, 1951 A. L. FREE HAL 2,573,762

RADAR RECEIVER SENSITIVITY coNTRoL SYSTEM INVENTORS ALBRT L FREIE ANDall BY f REMO/VD d /FFM/V AGEN 7' Patented Nov. 6, 1951 RADAR RECEIVERSENSITIVITY CONTROL SYSTEM Albert L. Free and D Philadelphia, Pa., as

e Breinond Homan, signers, by mesne assignments, to Philco Corporation,Philadelphia, Pa., a corporation of Pennsylvania Application March 27,1946, Serial No. 657,404

l- 6 Claims.

This invention relates to improvements in methods of and means forcontrolling the sensitivity of a superregenerative receiver employed ina radio ranging system of the general sort disclosed in copendingapplication of Wilson P.`

Boothroyd and Albert L. Free, Serial Number 651,888, iiled March 4,1946, Patent No. 2,536,- 488 granted January 2, 1951, assigned to theas` vsignee of the present invention, and of which this application isin part a continuation. In that application there is disclosed themethod of controlling the sensitivity of a superregenerative receiver asa function of the delay, with respect to a transmitted pulse. ofvariably delayed, produced pulses utilized to control the unquenching ofthe superregenerator to condition it for the reception of a reflectedsignal from an object at various ranges. Also disclosed are means forachieving this result, involving the generation of pulses of varyingwidths, timed with reference to transmitter pulses, and thedifferentiation of the trailing edges of these pulses to yieldotherpulses having characteristics varying as a function of the widthsof the generated pulses, which pulses, resulting from differentiation,were utilized to -control the sensitivity of the superregenerator.Although this arrangement yielded entirely satisfactory results undercertain conditions, it was found to. possess certain limitations. inthat, under certain circumstances, the achievable range of variation insensitivity was not sufficient.

Accordingly, the principal object of the present invention is to provideimproved methods of and means for controlling the sensitivity of asuperregenerative receiver employed in a radio ranging system, inaccordance with the same general method disclosed in the aforementionedcopending application and above referred to.

Specically'an object of this invention is to provide methods of andmeans for appreciably extending the range of sensitivity controlachievable in accordance with this general method.

Otherfeatures and advantages of the invention .will be apparent from aconsideration of the following specification and of the drawings, inwhich:

Figures l and 1A, taken together, illustrate the 'application of theinvention in one of its embodiments to a radar ranging system, and

Figures 2 and 1A, taken together, illustrate the application of theinvention in another embodiment to a radar ranging system.

Referring to Figures l and 1A, triodes 96 and 91 are connected to form acathode feedback 2 multivibrator pulse repetition frequency oscillator,which may be adapted to oscillate at a frequency of approximately 2,000cycles per second as adjusted by the variable resistor 98. Its circuitsshould be designed for maximum frequency stability and to give asuitable rectangular wave shape. Although its frequency may varysomewhat this will not affect the operation of the other circuits inaccordance with the invention. The negative pulse derived from the plateof tube 91 is supplied through a differentiating circuit comprisingcondenser 99 and resistor |00 to the grid of a trigger tube |36, theoutput of which will be a pulse corresponding to the trailing edge ofthe negative pulse derived from the plate of tube 91. This pulse is fedfrom the plate of tube I 36 to the grid of a trigger amplifier tube I0|and thence to the grid of a cathode follower modulator amplifier tube22|, from the cathode lload 222 of which a corresponding pulse issupplied through condenser 226 to the grid of modulator tube 236, whichmay be a type 3045 gas tube. The cathode follower tube 22| is used toprovide a low impedance drive for the gas tube 'modulator to avoidvariations in the time of its triggering. In the output circuit of themodulator tube 236 is connected a resonant charging choke |05 tuned bythe capacitors of delay line |06 which may have a characteristicimpedance of approximately 50 ohms and whose input is connected to theplate of the modulator tube in the manner shown. A modulating pulsewhich may be of the order of 2,200 volts is developed across resonantchoke |05 and is supplied. through delay line v|06 for shaping purposes,to the primary winding of pulse transformer |01. Included in thisconnection may be a transmission line 289 having a characteristicimpedance of approximately 50 ohms, since in practice magnetron |09, towhich the secondary of the pulse transformer |01 is connected. will belocated in a separate pressurized unit from the circuits heretoforedescribed. Magnetron |09 Imay be a type 2J39 tube operating in S bandwith a peak power output of approximately five kilowatts. Pulsedmicrowave energy from magnetron |09 may be supplied through a section ofstub-supported coaxial transmission line ||0 to a suitable radiating andreceiving antenna I. At suitable points along line ||0 may be locatedT-R cavity |I2 and capacity. probe ||3 for signal take-ofi, the exactfunctions of which will be explained in further detail hereinafter.

Negative pulse signals at the pulse repetition frequency of 2,000 cyclesper second are also 3 supplied from the plate of trigger tube |38 to theplate of tube 204, which together with tube 205 and associatedconnections comprises acathode feed-back, non-oscillatory multivibrator.The function of this multivibrator is to generate positive pulses ofvarying duration whose leading edges lcorrespond to the trailing edgesof negative pulses generated bythe P R. F. oscillator. Its mode ofoperation, is generally as follows: 'I'he grid of tube 200 is normallybiased more positive than the grid of tube 204 so as to cause tube 200normally to conduct. It should be noted, however, that the bias ontube'205 is determined-not only by the potential applied to its grid butalso by the drop in the cathode resistor 200 during the time the tube isconducting. Tube 204, on the other hand, is normally cut oil. Upon theoccurrence of a negative pulse supplied to it through connection ||4from the plate of tube |30, the grid of tube 205 will be drivensumciently negative to cut oil' the tube.. When this happens the cathodeoi tube 204 as well as the cathode o1' tube 200 will be reduced toground potential and tube 204 will begin to conduct. 'I'he current drawnby tube 204 will oi' course depend upon the bias applied to its gridfrom potentiometer 230. As tube 204 begins to conduct, its plate will gonegative and apply a negative impulse to the grid of tube 200 tomaintain it cut oil'. However this effect will gradually be overcome, ascondenser 201 charges through'tube 204, until a point is reached atwhich tube 205 again conducts. The circuit is then in condition torepeat its cycle in response to the next pulse supplied from the triggertube. The duration of pulses generated by this delay multivibrator willbe variable, depending upon the grid bias on ytube 204, from 1 to 14microseconds. From these varying width delay pulses a diierentiatedsignal is derived across the resistor 20| of a differentiating circuitcomprising this resistor and condenser 200, and the negative pulses,correspondinggto the trailing edges of the variable width pulses fromthe delay multivibrator, are supplied connection 202 to unquench asuperregenerative receiver whose circuits and mode o! operation will bedescribed in further detail vary, thereby,` varying the duration of thepulses generatedby the delay multivibrator from 1 to 14 microseconds 19times per second. In the absence of any,y received, reflected signal,the sweep tube will cause-the delay multivibrator continually tosweepthijough the range of pulse widths from` 1 |1014 microseconds,corresponding to ranges of from-1165 to-23 il|i ,yards. However a sweepcutoi! tilbe.=2 l 4, vvhich may` also be a type 2D21 gas tube, isconnected in shunt with condenser 2|6 and gisgsuppliedggthroughconnection 29| with pulsesfrom` the ,superregenerative receiver output.corresponding to received, target-reflected permit reducing the sweepvoltage to zero in order signals, to discharge the condenser 2 I0 by s.pre-` determined amount determined by resistor 2|! whenever such a pulseis received. 'I'he amount by which the condenser 2|6 is discharged bysuch a pulse is made such that the voltage to which the grid of tube 204of the delay multivibrator is reduced corresponds to a delay somewhatless than the time actually required for the preceding reilected signalto be received from the target.

a received pulse and unquenching of the super regenerative receiver, thelower end 24| oi' the cathode load comprising potentiometers 200 and 230may be connected to a suitable source of xcd positive potential. Thiswill prevent jamming of the system by a strongL continuous wave signalimpressed on the receiver circuits, which would normally cause the sweeptube to re continually, the sweep voltage to fall below the potentialcorresponding to minimum range andthe width of the delay pulse to bereduced to such an extent as to permit the receiver to pick up its owntransmitted signal. prevent the system from locking on targets closerthan a predetermined minimum range, such, for

example, as other friendly aircraft in a'formation.

Alternatively the same result might be achieved by connecting thecathode of a diode 242 to the would be achieved but an additional tubewould n be required.

Sweep tube 2|3 may also be provided in this embodiment with a specialform of in-switch to to select a new target at a shorter range. Thisswitching arrangement comprises a switch 243 normally connectingcondenser 244 to a source oi.'

sweep tube 2|3. The voltage developed across the condenser 244 willcause tube 2|3 to conduct heavily enough'to reduce the sweep voltage tothat corresponding to the minimum range of the system. The charge oncondenser 244 will be quickly lost and the sweep voltage will startagain in its normal manner. used to damp out the spark resulting whenswitch 243 is thrown. Condensers 244'and 246 in this arrangement mayeach have capacitanees 0f 600 ,up farads.

A range signal proportional to the peak voltage across condenser 2li maybe derived from divider" 239 in the cathode oi' tube 231 and may besupplied through connection 240 and relay contact 249 to a suitablerange indicator 200. Means may be provided for rendering range indicator295 inoperative in the absence of areceived target signal so that noindication will be given by it under these circumstances. The signal foractuating such a device can conveniently be derived from sweep cut-o1!tube 2|4 which draws current only in the presence of. a received targetsignal. Because of the high load'impedance in the plate circuit oi' thistube it can not be used as a source of power. Hence a peak de- 'I'hisfeature can also be used to Condenser 240 is y tector comprising diode240 and a high time constant load impedance consisting of condenser 252and resistor 253 may be connected to the plate of tube 2|4. The outputof this peak detector is supplied to the grid of tube 241, in the platecir- Consideration will now be given to the re-v ceiving circuits of thesystem which, as aforementioned, make use of superregenerativeprinciples. Received, target-reflected signals derived from T-R box H2are mixed with a signal from local oscillator |11 in crystal mixer |18and the resulting intermediate frequency is supplied therefrom throughtransmission line |19 to the input of buffer preamplifier tube |80. Itis to be noted that the primary function of this tube is to preventradiation through the antenna of signal from the superregenerator andthat, except for this requirement in certain military applications, thetube might be omitted inasmuch as suicient ampliiication is provided bythe superregenerator alone. In order accurately .to maintain thefrequency of the local oscillator |11, which may comprise a type 2K28klystron, an automatic frequency control circuit is employed. To thisend, received signals derived from another point on transmission line bymeans of capacity probe ||3 are mixed in crystal mixer 296 with localoscillator signal supplied through connection 294. 'I'he resultingsignal is amplified in a suitable intermediate frequency amplier 291 andsupplied to a conventional discriminator comprising double diode 298 andassociated circuits. From the output of the discriminator are derivedpositive or negative pulses, the polarity of which will depend upon therelation between the transmitter and local oscillator frequencies ascompared to the intermediate frequency tuning of the discriminator.These pulses are amplified in pulse amplifier tube 300 and are suppliedfrom the output thereof to the grid of a gas discharge tube 30|. Thelatter is connected in shunt with a second gas discharge tube 302 which,together with condenser 303, constitutes a sawtooth oscillator which maybe adjusted to operate at a low frequency of, for example, 5 cycles persecond. The voltage developed across condenser 303 is supplied throughconnection 304 to the repeller of local oscillator tube |11 to vary itsfrequency through a range comprising those frequencies which, when mixedwith frequencies within the range at which the transmitter mightoperate, will yield the desired intermediate frequency. Thus the gastube oscillator will tend to sweep the frequency of the local oscillator|11 through this range 5 times per second. However the positive pulsesfrom pulse amplifier 300, appearing on the grid of tube 30|, will causeit to conduct whenever the frequency of the transmitter exceeds thefrequency to which the discriminator is tuned. This will dischargecondenser 303 by a certain amount so as to tend to maintain the voltagethereacross, and hence rthe frequency of local oscillator |11, constant.

At the same time contacts 249 and a 6 The left hand triode section oftube 8|, m-

gether with tank circuit |82, comprises a superregenerative oscillatorwhich may be adjusted to operate at a. frequency in the neighborhood ofmegacycles. Pulses of intermediate frequency energy corresponding totarget signals will be supplied to tank circuit |82 through connection|83 and an inductor |84 coupled to the tank circuit inductance.Unquenching pulses at the P. R. F. rate, and variably delayed withrespect to transmitted pulses from the P. R. F. oscillator, are alsosupplied through connection 202 to a damping circuit comprising doublediode 203 and inductor |85 coupled to the inductor of tank circuit |82.As will be explained hereinafter, in accordance with the presentinvention-the characteristics of these unquenching pulses are varied asa function of their delay with reference to transmitted P. R.. F.pulses. As the delay of these pulses is varied cyclically in response tothe sawtooth wave generated by sweep tube 2|3, certain unquenchingintervals will be caused to coincide with received, object-reflectedtransmitted signals if the latter are present. In the presence of suchreceived signals oscillations in the tank circuit |82 will build up morerapidly, and to a higher level during'the unquench interval, than intheir absence. The rate of build-up of oscillations may be adjusted sothat, in the absence of received signal, they will not build up duringthe unquench interval beyond a. certain level, while, in the presence ofreceived signal, they will build up appreciably beyond this level Thisadjustment is conveniently made by adjustment of the coupling betweeninductor |84 and that of tank circuit |82, and by adjustment of thetuning of the circuit comprising inductor |84 and condenser 54 to differsomewhat from the resonant frequency of tank circuit |82. As will laterbe pointed out, the duration of the unquench interval is likewise animportant factor in controlling the difference between the output of thesuperregenerator in the presence and in the absence of received signal.As already mentioned the duration of this interval can readily becontrolled by differentiating or otherwise narrowing the pulsesgenerated by the quench oscillator multivibrator.

To distinguish between the output of the superregenerator with andwithout received signals, there is provided an integrator comprisingdiode 299, having its plate connected to a tap on the tank circuitinductance, and its cathode grounded through a suitable load impedancecomprising resistor I9| and condenser |92. rived thereacross isamplified in pulse amplifier 234 and is then supplied through connection29| to sweep cut-01T tube 2 I4 for the purpose hereinbefore described.

As explained in copending application of Albert L. Free, Serial Number652,320, filed March 6,

1946, Patent No. 2,476,409, granted July 19, 1949,

the no-signal output of the superregenerative receiver may be used tocontrol its sensitivity so as to maintain it at an average level whichis optimum for the reception of object-refiected signals. In the systemshown, automatic regeneration control voltage is derived from triode 2|1which, in turn, is supplied with the amplified output of thesuperregenerator from pulse amplifier 234 through cathode follower tube235. -Where, as in the system here described, the superregenerator isunquenched at the P. R. F.v frequency, it is essential that theoperation of sweep cut-off tube 214 (Figure 1) be adjusted so that, uponthe The output desimultaneous arrival of a received pulse with the thesweep voltage across condenser 2|. will be 'reduced by an amountsuilicient to prevent another such simultaneous occurrence during aninterval of duration corresponding to that required for the occurrenceof a substantial number (e. g. four) of successive unquenchings of thesuperregenerator. This will insure the A. R. C. voltage being dependentprimarily on the output of the superregenerator in the absence ofreceived signal, as desired, rather than on its output in the presenceof received signal. Also, as pointed out inthe copending applicationabove referred to, the time constant of the A. R. C. circuits should beadjusted so as to permitA the A. R. C. voltage to fall to the no-signallevel during the intervals between received pulses which arrivesimultaneously with the unquenching of the receiver when the system isadjusted as above set forth.

The foregoing description relates primarily to a radar ranging system ofthe sort to which the present invention is particularly applicable, andwhich has here been described at some length in order that the nature,mode of operation and applicability of our invention may be more readilyand fully understood.

Subject matter shown and described in this I specification but notclaimed herein is claimed in the following copending applications andpatent assigned to the assignee of the present invention as follows:

Application Number 651,398 of William E. Bradley, filed March 1, 1946,now Patent No. 2,536,346 granted January 2, 1951; application Number651,888 of W. P. Boothroyd and A. L. Free, filed March 4, 1946, nowPatent No. 2,536,488 granted January 2, 1951; application Number651,649, of K. H. Emerson, filed March 2, 1946,

4 now Patent No. 2,536,801 granted January 2, ,1951;

application Number 660,037 of W. E. Bradley, filed April 6, 1946; and U.S. Patent No. 2,476,409 of Albert Free, issued July 19, 1949.

In generalit may be said that, within certain limits, the greater theamplitude or the greater the duration of a given unquenching pulse, thegreater will be the sensitivity of the superregenerator during theinterval in which such a pulse is applied. The method of the differsfrom that set forth in the copending ap- 8 corresponding to themodulating pulse from trigger tube |0l. For convenience in illustrationthis has been omitted since it does not affect the mode of operation inaccordance with the invention. 'Ihe duration of this pulse is preferablymade somewhat less than the time interval corresponding to the maximumrange of target on which the system is to operate, and the pulseshoulddecrease in instantaneous amplitude from a time in each sweep cyclecorresponding to minimum range to a time later in the sweep cyclecorresponding to somewhat less than maximum range.

The shaped pulse thus derived is supplied through resistor 224 to thepoint of common connection between condenser 200, resistor 20|, and

connection 202 which normally supplies unquenching pulses from delaymultivibrator |00 7 to quench tube 203 (Figure 1A) of thesuperregenerative receiver. resistor 20| to divide the shaped pulse downto the proper amplitude and resistor 224 also serves to isolate shapingnetwork 222, 223 from diflerentiating network 200, 20|, the function ofwhich has already been explained. At 228 are represented unquenchingpulses generated by delay multivibrator |99, each delayed by a differentamount with respect to a given P. R. F. pulse. For convenience inexplanation there are all shown as if occurring in a single sweepinterval and as if the P. R. F. pulses to which each is related had allbeen translated in time and superposed without disturbing the spacingsbetweeny related P. R. F. and delayed pulses; it should be understoodthat actually the spacing between any two pulses is the spacing shownplus between any multiple of the P. R. F. period. At 229 is a'compositerepresentation of the eect of combining shaped pulses derived from thecathode circuit of tube 22|, and corresponding to different P. R. F.

0 pulses, with the variously \delayed unquenching pulses developedacross resistor 20| as shown at 220. Actually, for any given sweepinterval, the resultant waveform will consist of the combination of butone of the pulses shown at 22B-with a shaped pulse such as that shown at221. Quench tube 203 to which these waveforms are applied presentinvention plicationA in that it contemplatesvarying the ures 1 and 1A, arecurrent waveform at the 65 P. R. F. frequency may be obtained from apulse shaping network, comprising resistor 222 and condenser 223,connected in the cathode circuit of modulator amplifier tube 22|. Byproper adjustment of the values of resistor 222 and condenser 70 223there may be developed a shaped pulse corresponding to each P. R. F.pulse and of the generalform shown at 221. Actually the pulse developedwill differ from that shown at 221 in that .there will be a largepositive excursion at its peak will conduct during the intervals inwhich they exceed a predetermined potential level as established by therelative values of resistors 220 and 20| serially connected between asource of positive potential and ground. This will introduce dampinginto the tank circuit |82 of the superregenerator to inhibitoscillations therein. However, during the intervals corresponding to thenegative portions 230 of waveform 229 with reference to this' potentiallevel the superregenerator will be unquenched so as to permitoscillations to build up. It will be seen, therefore, that theeifect ofcombining the pulses 220 with the wave 221 is to modify the magnitudecharacteristics of the original pulses220 in the manner indicated at220. rBy reason of this.only the negative portions of the pulses 229,with `referencer to the predetermined amplitude level designated by thehorizontal axis in the diagram, will be effective to unquenchvthesuperregenerator.` and render it receptive to incoming reflections ofthe transmitted signals. Moreover, owing to the diiferences in lthemagnitude .characteristics Yof v Resistor 224 cooperates with 9generators, is subject to variation throughout a range which includesboth positive and negative values. It is only during the intervals ofnegative net conductance that the superregenerator will respond tosignals supplied to its input, and its sensitiviv at such times willdepend on the durations of the intervals of negative conductance and onthe magnitude of the net negative conductance during such intervals,which, in turn, are a function of the magnitude characteristics of thecontrollingl pulses.' Since these magnitude characteristcs have beencaused to vary as a function of pulse delay, in the manner above setforth, the' sensitivity oi the superregenerator will likewise be causedto vary as a function of this delay. For small delays, corresponding totargets at close range, the sensitivity will be low, while for largedelays, corresponding to more distant targets, the sensitivity will behigh. The manner in which the sensitivity varies throughout the rangeover which the system operates may be controlled by Varying the shape ofpulses derived from the cathode circuit of modulator amplier tube 22|.Although we have found a simple RC circuit suitable for our purposes inthe embodiment pulses are supplied through a resistor 353 forcombination with differentiated pulses from delay multivibrator |99developed across resistors 35| and 353 in series, which cooperate withcondenser 200 to form a differentiating network.

' The resultant waveform is supplied through conshown, it will beapparent that other and more complex shaping networks might be used toobtain a speciilc desired shape. It is not deemed necessary to showother such networks inasmuch as the use of various types of networks toshape signals of various waveforms to obtain other waveforms is wellknown.

For example only. in the embodiment shown, the modulator amplifier tube22|, from which .shaped pulses are derived, may comprise the twosections of a type 6J6 double triade-operated in parallel and thevarious circuit constants may be as follows:

Resistor 222 4,700 ohms Condenser 223 150 ,up farads Resistor 224 18,000ohms Resistor 20| 4,700 ohms Resiswr 225 ---i 470,000 ohms Condenser 22B1,000 mi farads In particular it was found desirable to make condenser228 small so that the low impedance from grid to ground caused by ringof modulator tube 236 would not impair the operation of the shapingnetwork 222, 223.

To avoid any possibility of confustion it may be well to point out thatthe present invention is concerned with controlling the sensitivity ofthe superregenerative receiver as a function of the range of a targetfrom which signals are to be received, whereas an aforementionedcopending application of Kenneth H. Emerson, Serial Number 651,649, ledMarch 2, 1946, Patent No. 2,536,801 granted January 2, 1951, isconcerned with maintaining the average sensitivity of thesuperregenerator at a particular level in response to the no-signaloutput of the receiver. methods of control are desirable, are consistentwith each other, and may be utilized to advantage in the same system as,in fact, they are in the one herein described.

Figures 2 and 1A illustrate a radar ranging system substantiallyidentical to that shown in Figures 1 and 1A, to which the invention isapplied in an embodiment differing from vthat of Figures 1 and 1A. Herethe waveform used to vary the characteristics of unquenching pulses as afunction of their delay is recurrent at the sweep oscillator frequencyrather than at the P. R. F. fre- Both nection 202 to unquench thesuperregenerator as in the previously described instance. Although therecurrent waveform has the period of the sweep oscillator it will havedifferent instantaneous amplitudes corresponding to diierently delayedunquenching pulses, and the waveform resulting from its combination withthem will produce substantially the same variation of the sensitivity ofthe superregenerator as was obtained using the arrangement of Figures 1and 1A.

Although our invention has been described with reference to a particularradar system, it is not to be regarded as limited to use with theparticular system shown. It will be apparent that it is applicable to avariety of other systems operating on the same general principles.Accordingly the scope of the invention is to be determined solely byreference to the appended claims.

We claim:

1. In a radio ranging system, a transmitter ot time-spaced pulsesignals, a superregenerative receiver including an oscillatory circuitand means responsive to control signals of variable magnitude suppliedthereto to vary the conductance of said oscillatory circuit throughout arange including positive and negative values as a function of thevariations in magnitude of said control signals, a producer of otherpulses for controlling the conductance of said oscillatory circuit,means for controlledly varying the time phases of said other pulses withreference to said transmitted pulses to produce controlledly phasedunquench pulses, a source of a signal of recurrent waveform, Whosevalues upon the occurrence of said controlledly phased unquench pulsesare a predetermined function of Said time phases thereof means suppliedwith said controlledly phased unquench pulses and responsive to saidsignal of recurrent waveform to modify the magnitude characteristics ofsaid unquench pulses in accordance with the instantaneous magnitude ofsaid recurrent waveform at the occurrence of said unquench pulses, andmeans for supplying said modified unquench pulses to said conductancevarying means to render the conductance of said oscillatory circuitnegative during intervals substantially coextensive with said modiiedunquench pulses. to an extent which is dependent upon the modifiedmagnitude characteristics of said unquench pulses, whereby to rendersaid receiver receptive to reflections of said transmitted pulses fromtarget objects during intervals substantially coextensive with. saidmodified unquench pulses and to control its sensitivity during saidintervals as a function of said.

modiied magnitude characteristics.

2. A radio ranging system according to claim l l, in which saidtransmitter is operative to transmit said time-spaced pulse signals at apredetermined repetition frequency, and in which said signal ofrecurrent waveform is recurrent atsaid predetermined frequency.

3. A radio ranging system according to claim 1, in which said source ofsaid signal of recurrent waveform is actuated to produce said last-namedAsignal in response to said time-spaced pulses from said transmitter.

4. In a radio ranging system, a transmitter of time-spaced pulsesignals, a superregenerative receiver including an oscillatory circuitand means responsive to control signals of variable magnitude suppliedthereto to vary the conductance of said oscillatory circuit throughout arange including positive and negative values as a function of thevariations in magnitude of said control signals, a producer of otherpulses for controlling the conductance of said oscillatory circuit,means for controlledly varying the time phases of said other pulses withreference to said transmitted pulses to produce controlledly phasedunquench pulses, means for selecting portions of said unquench pulseswhich are of certain polarity with reference to a predetermined`amplitude level, said last-named means being controllable to vary saidlevel of selection, a source of a signal of recurrent wave form whosevalues upon the occurrence of unquench pulses are a predeterminedfunction of said time phases thereof,

pulses with reference to said transmitted pulses,l

and means for supplying said selected portions of said unquench pulsesto said conductance varying means to render the conductance of saidoscillatory circuit negative during intervals substantially coextensivewith said selected portions to an extent which is dependent upon themagnitudes of said selected portions, whereby to render said receiverreceptive to reflections of said transmitted pulses from target objectsduring intervals substantially coextensive with said selected portionsof said unquench pulses and to control its sensitivity during saidintervals as a function of the magnitudes of said selected portions.

5. In a radio ranging system, a transmitter of time-spaced pulsesignals, a superregenerative receiver including an oscillatory circuitand means responsive to control signals of variable magnitude suppliedthereto to vary the conductance of said oscillatory circuit throughouta. range including positive and negative values as a function of thevariations in magnitude of said control signals, a producer of otherpulses for controlling the conductance of said oscillatory circuit,means for controlledly varying the time phases of said other pulses withreference to said transmitted pulses, a source of a signal of recurrentwaveform whose values upon the occurrence of said controlledly phasedpulses are a predetermined function of said time phases thereof, meansfor combining said controlledly phased pulses with said signal ofrecurrent waveform to yield a resultant signal, means for selectingportions of said resultant signal which are of certain polarity withreference to a predetermined amplitude level to yield modified pulseswhose magnitude characteristics vary as a function of their time phaseswith reference to said transmitted pulses, and means for supplying saidmodied pulses to said conductance varying .means to render theconductance of said oscillatory circuit negative during intervalssubstantially coextenslve with said modified pulses to an extent whichis dependent upon the magnitude characteristics oi' said modifiedpulses, whereby to render said receiver receptive to reections of saidtransmitted pulses from target objects during intervals substantiallycoextensive with said modiiied pulses and to control its sensitivityduring said intervals as a function of said magnitude characteristics.

6. In a radio ranging system, a transmitter of periodic time-spacedpulse signals, a superregenerative receiver adapted to receivereiiections of said transmitted pulses from target objects, saidreceiver including an oscillatory circuit and means responsive tocontrol signals of variable magnitude supplied thereto to vary theconductance of said oscillatory circuit throughout a range includingpositive and negative values as a function of the variations inmagnitude of said control signals, said receiver being subject toshock-excitation by said transmitter during predetermined time intervalsimmediately following each of said transmitter pulses, a producer ofother pulses of substantially uniformamplitude and waveform forcontrolling the conductance of said oscillatory circuit, means forcyclically varying the time phases of said other pulses with referenceto said transmitter pulses to produce controllably-phased unquenchpulses, said variation being such that at least some of said unquenchpulses occur during said intervals of shock-excitation of said receiver,a source of a signal of recurrent waveform periodic at the repetitionrate of said transmitter pulses and having values which decreasesubstantially exponentially with increases in said time phases of saidunquench pulses, means for combining vsaid signal of recurrent waveformwith said unquench pulses to produce a resultant signal comprisingmodified unquench pulses whose peak values differ from a predeterminedreference level -by amounts which are exponential functions of said timephases thereof, amplitude-discriminatory means supplied with saidmodified unquench pulses and operative to select only those portions ofsaid last-named pulses having predetermined polarity with respect tosaid reference level, and means supplying said selected portions of saidmodified unqench pulses to said superregenerative receiver to vary theconductance thereof.

ALBERT L. FREE. DE BREMOND B. HOFFMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,167,492 Sproule July 25, 19392,406,316 Blumeiin Aug. 27, 1946 2,407,198 Wolff Sept. 3, 1946 2,419,570Labin Apr. 29, 1947 2,421,340 Levy May 27, 1947 2,422,382 Winchel June17, 1947 2,460,202 Tyson Jan. 25, 1949 2,482,128 Schmid Sept. 20, 1949 YFOREIGN PATENTS Number Country Date 461,749 Great Britain Feb.r 23, 1947

